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Objectives: To investigate how responsibility interpretations regarding intrusions vary across the perinatal period and how this relates to obsessive-compulsive symptomatology. Design: A mixed design was used investigating differences in responsibility interpretations and omission bias between three groups (antenatal, postnatal, and non-childbearing) for baby-related and non-baby situations. Method: 94 women (26 antenatal, 35 postnatal and 33 non-childbearing controls) completed measures of various aspects of responsibility including responsibility attitudes, interpretations regarding specific intrusions and omission bias, as well as obsessive-compulsive symptomatology, anxiety and depression.

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The focus of this thesis is the much debated construct of impulsivity, exploring its meaning, etiology and measurement. The literature review provides a background for the empirical papers, by examining the theoretical underpinnings of impulsivity, from which a plethora of measuring instruments have been generated. The review explores the difficulties associated with measuring a contrast which has little consensus over its components, and highlights studies which have attempted to draw together a common understanding of the construct. The main paper provides a useful exploration of four widely used self-report measures of impulsivity, investigating whether the measures examine similar or different facets of impulsivity. The results demonstrate the lack of congruity between the measures, suggesting that two of the measures appear to tap a common construct, whereas the remaining two measure only a narrow construct and raise questions about its validity. The brief paper is a pilot study drawing upon a visual search paradigm to investigate the Attentional Fixity theory of impulsivity, arousal and performance among a sexual offending sample. The findings although tentative, failed to support the hypothesis that arousal improves performance in a cognitive task. Instead it was found that performance decreased when individuals were presented with sexual stimuli. The findings also fail to support the hypothesis that high impulsivity is associated with an inability to fix attention on a source of input. This suggest that the current sample of sexual offenders, as a high impulsive group tend to fix their attention on sexual stimuli and become distracted from other cognitive demands. Finally, the reflective review explores further findings from the empirical papers, reflecting upon methodological, ethical and conceptual issues.

Intrapersonal Externalities are outcomes from a decision which affect the payoffs from future decisions. Positive intrapersonal externalities represent self-investment in one's future self, such as learning a musical instrument or exercising. Negative intrapersonal externalities represent a disinvestment in one's future self, such as eating sugary food or smoking a cigarette. An individual who succumbs to the lure of an immediate payoff in lieu of future potential earnings is considered to be choosing myopically, and it is hypothesised that addictions are one such situation. This failure of the decision-making system to optimise its choices contrasts with delay discounting, in which an individual is assumed to choose rationally but to discount the future, and impulsive disinhibition, in which an individual is assumed to be unable to control their actions even while they state a preference for an action they do not take. This thesis starts by measuring the relationship between delay discounting and impulsive disinhibition with a range of addictive behaviours in a large online study, and finds that while they are consistent predictors there is further variance to explain. It then examines the validity of the intrapersonal externalities model, and finds that it adds independent variance beyond delay discounting and impulsivity in predicting smoking behaviour; there is no evidence that performance in intrapersonal externalities tasks is related to trait impulsivity. It also uses intrapersonal externalities in the laboratory to study advice seeking and taking in an impulsive decision-making context, which would be incompatible with delay discounting or impulsive disinhibition theory. This thesis concludes that the intrapersonal externalities model has been shown to be a viable third model to understand addictive decisions, and suggests that it could be extended to study social addictions.

Pathological gambling is a maladaptive behaviour associated with diminished self-control over persistent compulsive gambling behaviour despite negative consequences. A significant revision to the clinical perspective of pathological gambling is underway, and the disorder will likely be recognized as a behavioural addiction in the fifth edition of Diagnostic and Statistical Manual of Mental Disorders. However, the neurobiological, cognitive and behavioural processes that drive a ‘behavioural addiction’ are unclear. A series of five studies were conducted to investigate cognitive mechanisms associated with neural and behavioural substrates of addictive processes in disordered gambling. Studies 1 through 3 investigated neurobiological correlates of addiction in individuals with pathological gambling as compared to individuals with cocaine dependence, and as compared to non-addicted healthy controls. Study 1 investigated brain activity associated with anticipatory and consummatory reward processing during slot-machine gambling. Study 2 investigated executive control processes by examining functional brain networks associated with loss-chasing behaviour. Study 3 employed voxel-based morphometry (VBM) to explore alterations in grey-matter volumes in individuals with addictive disorders. Studies 4 and 5 investigated the behavioural substrates of addiction in regular gamblers utilizing emerging and novel research techniques. Study 4 examined continuous hand motion trajectories to explore approach biases and implicit processing. Study 5 employed an adaptive testing methodology to explore the influence of gaming machine preferences on cognitive processes and gambling behaviour. Research identified neurobiological and behavioural substrates of gambling-related beliefs and biases that indicate significant contributions of cognitive mechanisms to the development and persistence of a behavioural addiction. Results suggest addictive disorders may share some common features of anticipatory reward processing and brain structure (Studies 1 and 3), while neural signals associated losing outcomes and decision-making during gambling may be specific to disordered gambling (Studies 1 and 2). Furthermore, cognitive distortions in regular gamblers may influence reinforcement and executive control processes (Study 4), and individual preferences for gaming speed may influence cognitions and behaviour during machine gambling. As additional psychological disorders are being considered for classification as behavioural addictions, and clinicians will be faced with the challenges of treating individuals with these non-substance-related addictive disorders, a better understanding of behavioural addictions, through the study of disordered gambling, will be essential under the new diagnostic framework.